Arrays of microneedles were proposed as a way of administering drugs through the skin in the 1970s, for example in expired U.S. Pat. No. 3,964,482. Microneedle or microstructure arrays can facilitate the passage of drugs through or into human skin and other biological membranes in circumstances where ordinary transdermal administration is inadequate. Microstructure arrays can also be used to sample fluids found in the vicinity of a biological membrane such as interstitial fluid, which is then tested for the presence of biomarkers.
Despite much initial work on fabricating microneedle arrays in silicon or metals, there are significant advantages to polymeric arrays. U.S. Pat. No. 6,451,240 discloses some methods of manufacturing polymeric microneedle arrays. Arrays made primarily of biodegradable polymers also have some advantages. U.S. Pat. No. 6,945,952 and U.S. Published Patent Applications Nos. 2002/0082543 and 2005/0197308 have some discussion of microneedle arrays made of biodegradable polymers. A detailed description of the fabrication of a microneedle array made of polyglycolic acid is found in Jung-Hwan Park et al., “Biodegradable polymer microneedles: Fabrication, mechanics, and transdermal drug delivery,” J. of Controlled Release, 104:51-66 (2005).
Biodegradable polymer arrays have typically been used with water soluble drugs. The arrays are made using water soluble polymers that dissolve easily when inserted into the subject's skin. The use of water soluble polymers works well with water soluble drugs as a single phased liquid formulation can be formed.
With the advent of combinatorial chemistry and high throughput screening, the number of poorly water soluble drug candidates has dramatically increased. Poor solubility of the therapeutic agent is one of the most frequently encountered difficulties in the field of pharmaceutics.
Accordingly, it would be of benefit to develop an effective means of delivering therapeutic agents that are poorly soluble, have very low solubility in an aqueous medium, or are substantially water-insoluble via microstructures and of making use of the advantages of microstructure array delivery.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.